In stringed musical instruments such as guitars the neck region carrying the fretboard or fingerboard is typically made from wood; in some of the higher quality instruments the neck is reinforced by one or more longitudinal metallic truss members, which in accordance with longstanding conventional practice, are fully enclosed within the neck.
When a truss is provided, it is common to include some form of threaded truss adjustment means to control the truss tension so as to correct any curvature in the fingerboard, since generally it is desired to keep the fingerboard substantially flat for uniform finger stopping action on the strings. Such unwanted fingerboard curvature is typically concave, due to the strain induced in the neck by string tension, however the curvature may include an additional component due to residual warpage in the neck.
In conventional practice the adjustment means is accessible only from the front (ie. fingerboard) side of the instrument. Known art utilizing such construction has continued to suffer several drawbacks; in addition to the aesthetic compromises and adjustment difficulties arising from front-access adjustment, the practice of fully enclosing the truss poses a serious serviceability shortcoming: in the event the threaded adjustment means on the truss becomes stripped or the adjustment tool interface such as a screwdriver slot in the end of the truss rod becomes deformed to a point of malfunction, removal of the truss for repair or replacement is extremely difficult, and in fact may be practically impossible, rendering the instrument unrepairable.
Furthermore, most neck constructions of known art fail to provide reverse compensation capability for correcting convex fingerboard curvature.
In common contemporary practice, the truss is constrained in a curved disposition, fully enclosed within a channel formed from a composite neck structure which must be assembled from a plurality of component parts; typical three part configurations comprise (a) a main neck portion, a truss groove filler strip and a fretboard or (b) two half neck parts and a fingerboard part. In a known two part configuration, an arched truss is disposed along a non-uniform groove of varying depth routed in the main neck portion, enclosed by a separate filler part. In such composite structures, fabricating, assembling and fastening the various parts together imposes a substantial premium in the cost of producing the instrument.